Rot epidemic

[fanaticactus]

I was shocked upon going into the greenhouse a couple of days ago and finding a small P. magnifica had turned black on the crown and at the base. Near it I found a G. friedrichii was apparently rotting. I kept finding more and more of my collection had suddenly succumbed to rot. I can't figure out what I'd done wrong. When it came time for the first waterings after the winter dormancy, I did two or three light ones to 'wake the roots' as often said. Some of them so light that no water came out the bottom. Most of my substrate is now pumice, coir, a bit of rough gravel/sand and some earthworm castings (blended into finely milled sphagnum), so there's no actual soil to hold water in the pots. When I thought the cacti were ready, I gave the entire collection a thorough watering with a systemic to keep them pest-free, I had hoped. But you can see many mealies on the G. bruchii that had bloomed a few weeks ago, but it has been suggested that this particular one was infested with mites. The weather had been variable temperature wise and mostly sunny. During the cooler nights, I still kept a heater on low and turned it off during the days. On very hot days in the greenhouse, the vents opened and my ventilator fan was working. Most of them affected now are Mammillarias. By looking at these photos, can anyone discern anything signs that could suggest something else that caused this mass death? How can they rot with almost pure pumice in the pot? Of course I want to avoid such future events, so are there any suggestions for preventing this apparent rot?

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This M. elongata seemed to suffer the opposite fate: it dried up.

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The crown on this one is either rotting or is diseased. It almost looks burned.

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[adetheproducer]

The 4th picture does look like mites, get a systemic and treat it and separate from the rest of the collection. The rest do all look very sick, the only thing I can see they have in common is the soil. The blackening is typical of a fungal infection, can't remember the name of it off had at the moment but usually attacks weak plants so I think the cause is most likely a combination of water, temperature and drying time. Pumice can hold substantial amounts of water not just air so can keep things wet when looking dry, also coco nut coir is an organic substance, there will be fungi that will eat it and break down the cellulose so could be harbouring a particularly nasty local fungi that the cacti have no immunity of. Also you will know the coir floats which means by right it should hold a lot of air, if it get saturated with water it can hold it for far longer than you might think causing damp conditions around the roots . The gravel your are using could also be a source of unwanted organics, most smooth gravels are sourced from alluvial deposits so fresh water, these get coated in algi and silt so could be introducing high nitrogen to the soil providing good homes for bacteria and fungi which really you don't want around the roots. I would suggest (and will get some criticism for this as many don't agree) moving to a pure mineral mixture and re-potting the survivors. The temperature could also be a factor, I lost some plants to frost and they look very similar yours when they succumb to it, particularly the more tuberculate species which will collect condensation between tubercles which could have frozen during the winter and started the problem with the slow nature of the metabolisms they have only started to die and rot now. Sun scorch could also be a factor the last picture does look like sun burnt maybe the long winter and cooler spring meant when the sun finally came out it was too much for the plants. What ever the cause I would definitely think about getting them out of the pots inspecting roots for mealy infestations and smelling the potting mix, a fungal presence with have a obvious pong.

[Steve Johnson]

I was shocked upon going into the greenhouse a couple of days ago and finding a small P. magnifica had turned black on the crown and at the base. Near it I found a G. friedrichii was apparently rotting. I kept finding more and more of my collection had suddenly succumbed to rot. I can't figure out what I'd done wrong. When it came time for the first waterings after the winter dormancy, I did two or three light ones to 'wake the roots' as often said. Some of them so light that no water came out the bottom. Most of my substrate is now pumice, coir, a bit of rough gravel/sand and some earthworm castings (blended into finely milled sphagnum), so there's no actual soil to hold water in the pots. When I thought the cacti were ready, I gave the entire collection a thorough watering with a systemic to keep them pest-free, I had hoped. But you can see many mealies on the G. bruchii that had bloomed a few weeks ago, but it has been suggested that this particular one was infested with mites. The weather had been variable temperature wise and mostly sunny. During the cooler nights, I still kept a heater on low and turned it off during the days. On very hot days in the greenhouse, the vents opened and my ventilator fan was working. Most of them affected now are Mammillarias. By looking at these photos, can anyone discern anything signs that could suggest something else that caused this mass death? How can they rot with almost pure pumice in the pot? Of course I want to avoid such future events, so are there any suggestions for preventing this apparent rot?

Wow -- that's horrible, and I'm really sorry this is happening to you. Although I haven't worked with it, I think it'd be reasonable to lay blame on the coir and finely milled sphagnum. Ideally the soil component for a cactus mix should be sandy loam with little or no organic materials present. Unfortunately this seems almost impossible to find, and commercial potting soils these days are pretty horrible because they're heavily composted with every conceivable plant waste the manufacturers dump in. The following may be a viable alternative, so check this out:

http://www.ebay.com/itm/ARIZONA-EARTH-N ... 2a5107dce7" onclick="window.open(this.href);return false;

If you'd like, I'll contact the seller and find out exactly what's in their product. While I shouldn't be too excited yet, this could be the most promising thing we've seen coming down the pike in quite awhile.

By the way, I have to disagree with ATP on a couple of things. First, pumice dries out on a straight moisture curve over time, so it's not like your pumice was staying wet too long before it started drying out. That problem would be more likely coming from the coir and sphagnum (same as peat!). Second, I've been using gravel top dressings for years, and I have yet to see any evidence of algae there. Bear in mind that I live in a coastal microclimate with relatively high humidity all the time -- if I had any problem with algae, I would've encountered it a long time ago. With that said, I'll agree with ATP on going straight mineral. Among other things, your top dressings will dry out before they have the chance to develop algal blooms. Only reason for adding some soil to your mix would be if straight pumice dries out too quickly in your climate during summertime. The more I think about it, the more I'd like to pursue the Arizona Desert Naturals option for you. If it really is soil and not a bunch of composted organic crap, it could be worth a try. I'll keep you posted.

[fanaticactus]

I appreciate very much the detailed responses from ATP and Steve. I am soooo confused now about a proper substrate ]. It seems that when I was mixing added gravel, sand & perlite into soil from those 'standard' cactus potting soil bags, it was still too heavy and remained wet too long. Then I found this site and read all the 'ideal' potting soil recipes I could find and started using them. I asked about sterilizing soil and gravel in the micro or the oven and got mixed comments. Add to my confusion. Then coir seemed all the rage because it was fibrous and was supposed to keep just the right amount of moisture around the roots. I never used it exclusively but mixed it with pumice, which I gathered was a cure-all by all its fans in the Forum. I started that last year. It appears to have worked very well with some cacti, but now maybe not at all with others. Through all of my experimentation the advice about using NON-organic materials was an important theme to avoid decomposition, which leads to too acid a soil; but I understood that coir was the least likely to decompose to a risky stage. I just don't know what to do now.

So, Steve, I would be interested to know more about that 'Arizona Earth' if you can find out more. Very kind of you to suggest it. At this stage, should I consider any yellowing of the crown of a cactus a good sign that there is rot imminent?

I find it almost illogical that my outdoor cold-hardy cactus garden way up here in Vermont is more reliable and doing better that so much of my collection in the very expensive, custom-built greenhouse.

[spikef35]

That's bad I got the same rot a few weeks ago it's devastating it's likely your soil I use the worst soil likely on this forum I used to use cacti soil Kent for the ground now I'm switching to potted premium cactus soil I'm going to have to recremend a huge and drastic way of treatment first de pot everything! If your collection is less than 200 plants it might be easy next check for fungus and spray cacti with a fungicide and mix the soil keep them bair root in the sun for a few days Same with the seperated soil wait for the fungacide to become light safe and bame

[Steve Johnson]

Any sudden changes on cacti are never good, and that would certainly be the case with yellowing at the crown. IMO coir and peat/sphagnum are the worst ingredients going into a mix for desert cacti, and they both have the same problem -- takes a long time to wet, but once the stuff gets saturated it takes forever to dry out. If I get a useful response from the Desert Earth Naturals people, I'll give you some feedback.

[fanaticactus]

Any sudden changes on cacti are never good, and that would certainly be the case with yellowing at the crown. IMO coir and peat/sphagnum are the worst ingredients going into a mix for desert cacti, and they both have the same problem -- takes a long time to wet, but once the stuff gets saturated it takes forever to dry out. If I get a useful response from the Desert Earth Naturals people, I'll give you some feedback.

Thanks, Steve. Now I'm so afraid of every possible microorganism that could be in any soil or even gravel I use, should I go back to sterilizing everything in the oven? I really hate the prospect of that because it's so time-consuming.

[BarryRice]

I wouldn't focus on sterilizing. Even if you do, once you introduce the soil to your pots organisms will arrive.

[fanaticactus]

I wouldn't focus on sterilizing. Even if you do, once you introduce the soil to your pots organisms will arrive.

Well, I like the idea of not having to sterilize, Barry, but don't like the fact that microorganisms will probably be introduced no matter what. It would be wonderful to be able to have just ONE year when I don't have a catastrophe. I don't know how the rest of you do it and always manage to have such beautiful, healthy displays. Granted, many of you live in areas much more friendly to cactus growing with better access to more ideal native soil than mine.

[fanaticactus]

This morning I just dumped most of the rotted ones and, except for one pot whose substrate was just slightly damp, the substrate in all the pots was dusty dry. So now I'm really puzzled.

[iann]

Eek! Maybe you just found all the plants that lost their roots over winter. They would have been sitting in damp soil since you watered, nothing to take the water away.

[fanaticactus]

Eek! Maybe you just found all the plants that lost their roots over winter. They would have been sitting in damp soil since you watered, nothing to take the water away.

To be honest, a couple did not have roots; the others seemed OK. I hadn't watered the collection since late last September, I believe. But I started repotting with pumice and coir mid-to-late summer. Perhaps that was not a good idea. From now on, if I don't repot by mid-July or thereabouts I think I should let them go until the next Spring.

[keith]

I have had cactus die like that. I call it Orange Rot. They get wet roots and cold and down they go. It sucks. Too much water ( usually winter) and not drying out fast enough is the cause of 90% of my cactus death when they die like your picture shows. I lose a few cactus ever year to orange rot.

Like when the wind blows over a entire cactus bench in December and I have to re-pot in December.

" How can they rot with almost pure pumice in the pot?" From the pics U posted its not pure pumice I see little pieces of wood ? Choir? Store bought soil ? Some cactus from S. America probably would grow fine in store bought soil. Mammillarias some would be Ok I guess ?

Anyway if it floats I don't use it in "most" of my cactus soil mix. Sometimes a few pieces of Pumice float or some tiny pieces of organic that's OK. Sterilizing the soil I don't do that because it wipes out any balance you have of micro organisms in the soil. Plus what a pain if you use a microwave oven. Even for seedlings I don't do it I just use hydrogen peroxide.

[fanaticactus]

" How can they rot with almost pure pumice in the pot?" From the pics U posted its not pure pumice I see little pieces of wood ? Choir? Store bought soil ? Some cactus from S. America probably would grow fine in store bought soil. Mammillarias some would be Ok I guess ?

Thanks for your input, keith, and sorry you've lost a number of cacti to rot. Yes, there are a few pieces of twigs, wood, whatever was in the bagged soil I used for just a few cacti. Most Gymnos like a bit of organic in the mix, as do a few Mamms, but almost all that got repotted late last summer were in a mix of pumice, a bit of gravel and a handful of earthworm castings as a mild fertilizer. According to the ingredients on the bag, the castings are added to some finely milled sphagnum which helps it mix in more evenly with soil.

[fanaticactus]

All those pictured above have been dumped. I separated most of the other ones for which there's no hope and here they are. You'll notice some that had bloomed nicely earlier. Undoubtedly, there will be others to follow. The most likely explanation (offered by my Forum friend, Steve Johnson) is an application of a systemic before the roots became fully functioning, although I had already watered the entire collection lightly a couple of times. Sad that I had to lose some nice plants but looking forward to starting anew. Live and learn!

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